The present invention relates to lubricants and, more particularly, to lubricating compositions especially adapted for use in conjunction with projectiles and firearms and methods of applying such lubricants.
This invention is also directed to a method of coating bullets to reduce the "leading effect" thereof on bores of firearms through which the bullet is projected and to preventing fouling of automated equipment used for loading bullets into shell casings therefor.
One of the more important problems with unjacketed bullets is known as "leading," which is the phenomenon of lead from the bullet being deposited, by melting or otherwise, on the interior surfaces of the gun barrel. When this occurs, it is difficult to fire the bullets accurately and consistently even with exactly matched loads in a firearm even from a fixed position. The performance of bullets is of utmost importance to those policemen and soldiers whose very lives depend on their bullets' performance. In an attempt to overcome the detrimental effects of leading, commercial ammunition manufacturers and individual hand loaders have adopted various expedients. One of these consists of jacketing or partially jacketing the lead bullet with gilding metal, a copper base alloy nominally containing 5 percent zinc. Unfortunately, while the jacketed bullet is a significant advance in the art, it too has disadvantages, the more important of which include expensiveness and "copper fouling"; i.e., the transferance of copper from the bullet to the inner surface of the barrel. Recently aluminum jacketed bullets have been introduced for pistol and revolvers to solve the leading problem at reduced cost and yet allow suitable upset upon impact. Yet, this round is not suitable for rifles where bullet velocities are high enough to cause aluminum fouling.
It becomes apparent that the foregoing improvements have not been complete answers to all of the problems besetting the marksman. Indeed, the proposed solutions to many of the problems have not only frequently raised difficult new problems but also have served to emphasize the problems remaining unsolved. For example, friction was once considered to be such a small factor of ballistics that it was often ignored. Now, the opposite is true particularly since it is known that even a relatively low velocity can create sufficient frictional heat to actually melt the surface of a lead bullet and cause leading in the barrel and lead gases to be produced. Furthermore, gun barrel imperfections even though microscopic in size can cause small particles of metal jackets, zinc bases or lead to become embedded in the surface of the barrel. Continued firing only creates additional deposits which can shift positions within the barrels resulting in erratic trajectories.
Efforts to counteract frictional forces with most prior art wax lubricants have not been too successful particularly where the was lubricant selected is a candle wax or one that has been employed to combat frictional effects in a non-ballistics application. A probable reason for the failure of such a wax lubricant may be traceable to the sometimes severe conditions encountered in shooting a firearm where bullet velocities may be as high as 3,000 or 4,000 feet per second and where pressures on the bullet may be as high as 50,000 pounds per square inch. In addition, many of the prior art wax lubricants, including those intended for ballistics applications, are nothing more than greased wax compounds. These lubricants are unstable at the frictional temperatures and pressures encountered by a bullet rapidly traveling through a gun barrel. Furthermore, the prior art greased wax compounds are tacky and thus tend to pick up grit and sand particles which can contribute to, rather than inhibit, barrel wear. Some of the other prior art wax lubricants suffer from the disadvantage of being too costly or too difficult to apply to either the firearm or the ammunition.
The whole broad problem of providing a suitable wax lubricant for ballistics applications is rendered even more difficult by the necessity that the lubricant possess a formidable array of anomalous characteristics. For example, it should be noncorrosive to both surfaces it is to lubricate. It should remain stable over the entire temperature range encountered in ballistic applications. It should be fairly inexpensive. It should have the capacity to tenaciously fill any pores in the barrel and yet provide a fairly smooth surface.
Although many attempts were made to overcome the foregoing difficulties and other disadvantages, none was entirely successful when carried into commercial practice.
In addition to the ballistic considerations above there are production considerations. As noted above, it is a common practice in loading bullets into shell cases to coat each bullet, prior to loading, with a lubricant to reduce the "leading effect" of the bullet on the bore of the firearm through which the bullet is projected. The most commonly used lubricant is beeswax which presents a problem in that a residue of the beeswax slowly builds up on the loading mechanism of automatic equipment used to load the bullets into the shell cases. This residue eventually clogs the mechanism to the point that it requires curtailment of production for the purpose of disassembling the loading equipment for cleaning. It has remained a problem to find suitable compositions for coating bullets without at the same time creating problems in use of automated loading equipment.
In addition to the above concerns there is the more recent recognition that improperly ventilated indoor ranges can develop sufficient levels of lead gases under intensive shooting conditions to be a possible health hazard unless the bullets are coated or jacketed.
Yet, those precise ranges have a maximum need for inexpensive target ammunition so any such coating or jacket should be cheap to make so that ranges can shoot a maximum number of rounds within a given ammunition budget without health hazards.
One proposed solution, as per U.S. Pat. No. 4,196,670 issued Apr. 8, 1980 to M. K. Vartsvog, was a method for coating bullets with a non-wax composition which, it was claimed, reduces the "leading effect" of the bullet on the bore of a gun without, at the same time, fouling the mechanism of automated equipment used for loading bullets into shell casings therefor. The Vartsvog composition contained molybdenum disulfide dispersed in a suitable carrier therefor such as a synthetic resin which is dissolved in a volatile hydrocarbon solvent. The coating was allowed to dry on the bullets by evaporation of the volatile solvent before loading the coated bullets into shell cases. However, this second method has the obvious drawback of requiring hazardous volatile solvents to be used with the resultant added costs of extra safety equipment.
A similar approach which substituted the well-known lubricant coating Nylon 11 or other conventional lubricant coating such as polyethylene, together with the conventional additive molybdenum disulfide in powder form onto a pre-heated bullet, is taught by Oberg, et al. U.S. Pat. No. 4,328,750 issued May 11, 1982. However, this latter method has the drawback that MoS.sub.2 tends to separate out of the mix, thus requiring continual agitation. Also, high bullet heats are required since the bullet heat is used to melt the coating powder. Also the powder is applied by fluidized bed reactors which require high volume air supplies, are expensive and require maintenance.
A previous attempted solution to the problems, also utilizing MoS.sub.2 grease as an additive to paraffin wax was that of U.S. Pat. No. 3,356,029 issued Dec. 5, 1967 to J. V. Seidel wherein the lubricating compositions contain, on a weight basis, paraffin wax and wheel-bearing grease (e.g. a lime soap thickened lubricant) in a ratio of between 0.8:1 and 1.2:1 with the balance essential discrete particles of molybdenum disulfide (MoS.sub.2) in amounts of at least 2 percent but not more than 20 percent, e.g., 5 percent to 20 percent, the lubricating composition is a substantially homogenous mixture of wax and grease with the MoS.sub.2 substantially uniformly dispersed there through, and the ratio of paraffin to grease is advantageously 1:1. However, the production problems noted above are not addressed by the composition of the Seidel patent, and a messy MoS.sub.2 grease must be introduced to the process with resultant extra cleanup effort being required.
From the above, it becomes apparent that the existing lubricants still have many drawbacks and a better lubricant is needed.
Applicants have unexpectedly been able to provide a non-migratory, flexible, high melting point, high vapor pressure, strongly adhesive, modified wax lubricant without even requiring molybdenum disulfide additions, although MoS.sub.2 could be added if desired. Specifically applicant provides a bullet lubricant which comprises from about 3 percent to about 10 percent by weight of low molecular weight polyethylene in a wax base.
In another aspect, the invention provides a method of lubricating a bullet, which method comprises the steps of:
(a) heating the bullet to a temperature within the range of from about 180.degree. F. to about 330.degree. F.; PA1 (b) heating a lubricant mix comprising at least 3% by weight low molecular weight polyethylene polymers in a wax base to a temperature within the range of from about 250.degree. F. to about 300.degree. F.; PA1 (c) coating said heated bullet with said heated lubricant mix; PA1 (d) removing excess lubricant from said bullet; and PA1 (e) cooling said coated bullet to a temperature below the melting point of the wax base to solidify said coating. PA1 (a) crystalline to microcrystalline structure; PA1 (b) capacity to acquire gloss when rubbed (distinction from greases); PA1 (c) capacity to produce pastes or gels with suitable solvents or when mixed together with other waxes; PA1 (d) low viscosity at just above the melting point (distinction from resins and plastics); PA1 (e) low solubility in solvents for fats at room temperature.
The advantages of the invention will be better understood upon reference to the following detailed description.